"It looks like he'll be out for the year," Harbaugh said of Williams at the start of his weekly news conference. "Disappointing."

Williams suffered the injury Sunday night in the first quarter of the 49ers' 29-3 loss. Seattle's J.R. Sweezy cut blocked Williams while he was engaged with another offensive lineman.

Veteran Glenn Dorsey moves into Williams' starting spot for now. Harbaugh said the 49ers are exploring ways to add depth at that position.

Dorsey is the only listed nose tackle on the 49ers' 53-man roster. One-time options Will Tukuafu and Lamar Divens can't be brought back because they were waived/injured. Mike Purcell is on the team's practice squad, and he could be signed to the active roster before Sunday's game against Indianapolis.

"We're looking through that right now, and we'll make a decision in the next day or two," Harbaugh said of a potential move that likely would coincide with Williams being placed on season-ending injured reserve.

As it stands, Dorsey is thrust into a prominent role for the first time as a member of the 49ers, who signed him in March as an unrestricted free agent. He is accustomed to the spotlight, having starred for LSU and being selected fifth overall in the 2008 NFL draft by Kansas City.

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"Glenn played well," Harbaugh said of Dorsey's performance Sunday, which included a sack. "He had a lot of good snaps."

Harbaugh on Sunday termed Sweezy's low block on Williams a legal play. On Monday, he termed it an "unfortunate play."

The players had the day off Monday, so neither Williams nor any of his teammates was available for comment.

Free safety Eric Reid is in the process of going through the league-mandated protocol for players who suffered a concussion.

"The good news is, he's not symptomatic today," Harbaugh said of Reid.

Reid, who left Sunday's game with a concussion, can't return to practice or play in a game again until he passes a series of tests.

Tight end Vernon Davis, who suffered a hamstring injury Sunday night, will be examined to determine the extent of his injury, Harbaugh said.

Harbaugh didn't provide an update for defensive lineman Ray McDonald, who suffered an ankle injury in the fourth quarter.

Colin Kaepernick statistically, at least, turned in the worst game of his brief NFL career, yet Harbaugh praised his starting quarterback.

"He played the best and was the most productive person we had on offense," Harbaugh said of Kaepernick.

Kaepernick completed only 13 of 28 passes for 127 yards and no touchdowns. The Seahawks intercepted three of Kaepernick's passes, including one near the goal line, and sacked him three times. Kaepernick also lost a fumble and finished with a passer rating of 20.1.

"I'm not disappointed in the way Colin played at all," Harbaugh said. "He did what he could."

Harbaugh pointed out that both quarterbacks struggled as a result of playing against two of the league's best defenses.

Sure enough, Seattle's Russell Wilson misfired on all six passes before the game was delayed an hour because of lightning, and he had one of his 19 passes intercepted and was sacked four times.

The 49ers' penchant for breaking the rules continued Sunday, when they were penalized 12 times for 121 yards. Through two games, the 49ers are the league's second-most penalized team with 23 for 206 yards, behind only the winless Tampa Bay Buccaneers (26 for 220).

"That's an area that obviously we need to improve on," Harbaugh said. "Hopefully we'll see significant improvement this week."

Davis offered a stark assessment shortly after Sunday's game.

"If any team continues to stock up the penalties, just penalty after penalty, it can cost you the season if you do it every game," Davis said. "But we're not going to allow that to happen. We're better than that. It was just a game where we just acted instead of thinking."

The 49ers committed five turnovers and scored no touchdowns in a game for only the third time since start of the 1979 season. They also pulled off the dubious accomplishment in 1999 against the Jacksonville Jaguars and in 2005 against the Colts.